''Rhipaeosaurus'' is an extinct genus of nycteroleterid parareptile known from an articulated skeleton from the mid Middle Permian of European Russia. It contained a single species, ''Rhipaeosaurus tricuspidens''. A Bayesian inference in phylogeny, bayesian analysis suggests that it is more closely related to pareiasaurs than to the other nycteroleterids, due to skull and tooth features. For this reason, "Nycteroleteridae" may be a Evolutionary grade, grade rather than a clade, unless redefined to exclude ''Rhipaeosaurus''.

Description

''Rhipaeosaurus'' is around a meter long, larger than any other "nycteroleterids" and closer in size to later pareiasaurs. Postcranial remains were similar to ''Macroleter'', though the limbs were more robust and the ankle bones were unfused. The teeth were flattened and tricuspid (possessing three Cusp (anatomy), cusps), seemingly intermediate in form between the one- or two-cusped teeth of earlier nycteroleterids and the multi-cusped teeth of pareiasaurs. Many components of the partial skull and skeleton (which was originally fairly complete) had been lost or degraded between 1940 and 2012, obscuring most aspects of its anatomy.

History

''Rhipaeosaurus'' was first described in 1940, from a fairly complete skeleton found in the Ural Mountains of Russia. The name 'Rhipaeosaurus' comes from 'Ῥιπαεος' 'Rhipaeos, a range of mountains in Greek mythology thought to be the Urals, and '', meaning 'lizard'. 'Tricuspidens' refers to its three-cusped teeth. ''Rhipaeosaurus Taxonomy (biology), taxonomic history has been full of difficulties. At first it was placed in its own Family (biology), family, the Rhipaeosauridae, and considered the type species. Other taxa, such as ''Parabradysaurus'' and ''Leptoropha,'' later joined it in this family. However, when more remains of these additional taxa were found, they were determined not to be rhipaeosaurids at all. ''Parabradysaurus'' was found to be an Dinocephalia, estemnosuchid, more closely related to mammals, and ''Leptoropha'' was identified as a Seymouriamorpha, seymouriamorph amphibian. ''Rhipaeosaurus'''s status as a parareptile is still considered relatively stable, either as a basal nycteroleterid or a transitional taxon between other "nycteroleterids" and pareiasaurus.

References

External links

The Paleobiology Database

Permian reptiles of Europe Pareiasauromorphs Fossil taxa described in 1940 Prehistoric reptile genera {{paleo-reptile-stub